As the semiconductor industry continues to reduce package dimensions, foundries are looking to increase vertical density in addition to horizontal circuit density. 3D packaging saves space by stacking separate chips in a single package. This packaging, known as System in Package (SiP), uses off-chip signaling (e.g., by way of conductive paths in the package substrate) for communication between chips in the package The chips are not integrated into a single circuit. Rather, the chips within in the package communicate as though they are mounted in separate packages on a normal circuit board. For example, both the upper and lower chips may be wire bonded to the package substrate.